1. Field of the Invention
The invention relates generally to the forming of glass sheets and, more particularly, to a bending mold having side mounted weight assemblies for shaping hot glass sheets into curved shapes.
2. Description of the Prior Art
In the shaping of hot glass sheets, it is common practice to use a contoured, metal bending mold that supports a flat glass sheet and conveys it through a heating lehr, such as a tunnel lehr. An example of one such heating lehr is disclosed in U.S. Pat. No. 4,804,397 to Stas et al., which disclosure is herein incorporated by reference. As the temperature of the glass sheet increases and approaches its heat softening temperature, the sheet begins to sag under the force of gravity and conforms to the contours of the mold. The bending mold with the shaped glass sheet is then conveyed out of the lehr to cool.
Some conventional bending molds also include hinged or articulated end sections to help facilitate bending the sides of the glass sheet into sharp curvatures that could not normally be obtained through normal sag bending techniques. An example of one such articulated bending mold is disclosed in U.S. Pat. No. 4,687,501 to Reese, which disclosure is herein incorporated by reference. These articulated bending molds usually include a main frame having a central portion flanked by two pivoting end sections. Each end section is pivotally mounted on a pair of hinge blocks extending outwardly from the front and rear of the main frame. A pair of weight arms are connected to each end section inboard of the hinge blocks and extend along the front and rear of the central portion of the mold. The weight arms are configured to bias the end sections upwardly under the influence of gravity when the glass sheet reaches its softening temperature to shape the glass sheet.
While generally acceptable for bending and shaping glass sheets, such conventional articulated bending molds have limitations. For example, two weight arms are mounted on the leading edge of the mold as it moves through the lehr and are attached to the respective front ends of the end sections inboard of the front hinge blocks. Two additional weight arms are mounted on the trailing edge of the mold and are attached to the respective rear ends of the end sections inboard of the rear hinge blocks. These weight arms and hinge blocks typically extend several inches beyond the leading and trailing edges of the bending mold, increasing the overall length of the bending mold.
In a conventional bending process, overall productivity depends, among other things, upon the number of bending molds which can be processed through the lehr in a given period of time and thus the spacing between adjacent molds being conveyed through the lehr is a significant factor. Because of the leading edge and trailing edge mounted weight arms and hinge blocks of the prior art, adjacent bending molds must be spaced relatively far apart in a tunnel lehr thereby decreasing the number of bending molds which can be moved through the lehr in a given period of time.
Additionally, the conventional mounting of the hinge blocks and weight arms of the prior art results in four weight arms and hinge blocks located between the glass supporting portions of adjacent bending molds as the molds move through the lehr. This mass of metal absorbs and radiates heat differently than the glass sheets, adversely impacting the heating uniformity of the lehr.
Further, conventional weight arms typically have a relatively long attachment length between the weight and the hinge block and thus the weight arms flex, which can adversely impact upon the force being applied to the ends of the end sections, adversely impacting the final shape of the glass sheet and resulting in the rejection of the shaped glass.
As can now be appreciated, it would be advantageous to provide bending molds and methods of bending glass which do not have the drawbacks or limitations of the presently available bending molds and methods.